Method and system for controlling cooperative object-transporting robot

ABSTRACT

A control of a cooperative object-transporting robot which transports an object in cooperation with a man. The robot shares substantially a half of the weight of the object with the man, while the object is kept in a horizontal posture. A force applied to the robot by the object is detected by a force sensor, and based on the signal from the force sensor, a motion instruction is output for the motion components by the rotational force component τ 1  around the horizontal axis and the translational force component Fx 1  in the horizontal back-and-forth direction, upon setting a gain to reduce the resistance forces of the robot to small values. The translational force component F y  in the direction of the object short axis is constrained so that no translational motion in the direction of the object short axis occurs.

TECHNICAL FIELD

The present invention relates to a method and system for controlling acooperative object-transporting robot usable in heavy article transportoperations in the mining and manufacturing industries, the agriculture,forestry, and fishery industries, the construction industry, thedistribution industry, homes, etc.

BACKGROUND ART

One of object-transporting methods in which a man and a robotcooperatively transport an object, is a method called “power assist”which has been studied by the California University, the TohokuUniversity, the Mechanical Engineering Laboratory of the Agency ofIndustrial Science and Technology, etc. This is a technique in whichthere are provided two force sensors for detecting the load of an objectgrasped by the tip of a robot arm and a force applied by an operator,respectively, and in which the robot reduces the load of the operatorwhile moving so as to copy after the motion of the operator, byamplifying the force applied by the operator and then applying theamplified force to the object.

However, in accordance with this method, it is necessary for theoperator to grasp a force sensor handle disposed at the tip of the robotarm and to move it, and hence the place where a force can be applied islimited to only one portion of the object. When transporting a longobject or a large-sized object, as shown in FIG. 1, it is desirable thata hand 2 attached at the tip of the robot arm 1 and a human operator 3grasp, for example, each of the ends of the object 4 and support theobject 4. However, in this case, while a force can be measured on therobot arm 1 side by providing a force sensor 5, a force applied to theobject 4 cannot be directly measured on the operator 3 side. This makesit difficult to apply the above-described “power assist” technique.

On the other hand, the Stanford University in U.S., the TohokuUniversity, etc. has studied a method in which a man and a robot supportan object at some portions thereof and in which they transport theobject while sharing the load therebetween. This method is primarilybased on impedance control. Specifically, in this method, an object issupported under weightless conditions by compensating for the weight ofthe object, and simultaneously virtual impedances (inertia, viscosity,and spring coefficient) are set with respect to the object or the robot,whereby the motion of the object is changed in response to the change inthe force applied by the man, and the motion of the object is caused tocopy after the motion of the man.

In order to compensate for the gravity acting on the object, however, itis necessary to know in advance the mass or the mass distribution of theobject. This hinders this method from being flexibly applied to thetransportation of various objects.

When the object is a long object, it is virtually only a translationalforce which a man can apply. It is difficult to apply a torque(rotational force) to one end of an object to be transported. In thecase of a control based on impedance control, a straight-ahead motion inthe direction of the long axis obtained by connecting the man and therobot is easy, but with regard to a motion including rotation, it isdifficult for man to positionally control the end point of the robotside as a target point. In order to move the body by applying a smallforce, it is necessary to set impedance parameters such as inertia andviscosity to be low values. In this case, however, a drift (slippingmotion) in the normal direction is generated, and the drift is difficultto stop. This raises a problem that it is difficult to intuitivelyforecast behavior of the object.

The reason that the above-described problems associated with theconventional art is caused is because the impedance parameters are setto be uniform in all directions, and also they are set to be in anabsolute coordinate space. As a result, behavior of the object becomesone which man has never daily experienced, so to speak, a case like asif the object floating in a weightless space were moved by a forceapplied. This makes operations of making the object reach a targetposition and posture difficult.

DISCLOSURE OF INVENTION

It is an object of the present invention to solve the above-describedproblems, and to achieve a controlling means for making the arm of acooperative object-transporting robot share approximately a half of theweight of an long object, in the robot control in which a man and therobot grasp each of the ends of the long object, sharing the load due tothe weight thereof.

It is another object of the present invention to achieve a controllingmeans for a cooperative object-transporting robot, the controlling meanshaving only to have one sensor for measuring a force applied to therobot arm by an object, as a force sensor, without the need to have asensor for measuring a force by an operator, and the controlling meansnot being required to know the dimensions and the mass of the object inadvance.

It is still another object of the present invention to permit a man tointuitively perceive the behavior of the object by the daily sensesthereof in the control for the above-described cooperativeobject-transporting robot, by simplifying the relationship between theforce applied by the man and the motion of the object by limiting thedirection in which the object is movable.

It is a further object of the present invention to achieve a controllingmeans for a cooperative object-transporting robot, the controlling meanspermitting a man to intuitively perceive the above-described behavior ofthe object by the daily senses, without deviating from the originaloperational purpose of making the object reach arbitrary target positionand posture.

In order to achieve the above-described purposes, the controlling methodin accordance with the present invention, which is essentially acontrolling method for controlling the cooperative object-transportingrobot in order that a man and the robot transport a long object or alarge-sized object while grasping each of the ends thereof, ischaracterized in that an angle of the hand-tip of the robot is detectedby angle sensors, and that, based on the sensor signals, a motioninstruction for a translational motion of the hand-tip in the verticaldirection is output so as to keep the posture of the object horizontal.

The above-described controlling method may be such that a force appliedto the robot by the object and an angle of the hand-tip of the robot aredetected by sensors, and that, based on the sensor signals, a motioninstruction to drive the robot arm is output for the rotational motioncomponent around the horizontal axis and the translational motioncomponent in the horizontal back-and-forth direction, upon setting again so as to reduce the resistance forces of the robot to small values.

On the other hand, the controlling system in accordance with the presentinvention is essentially a controlling system for controlling thecooperative object-transporting robot in order that a man and the robottransport a long object or a large-sized object while grasping each ofthe ends thereof, and is characterized by angle sensors for detecting anobject-grasping angle of the hand-tip of the robot, a motion convertingpart for outputting the motion component of the hand-tip in the verticaldirection so as to keep the posture of the object horizontal, based onthe hand-tip angle detected by the angle sensors, and a coordinateconverting part for outputting a motion instruction to drive the robotarm, based on the above-mentioned motion component.

The above-described controlling system may comprise a force sensor fordetecting a force applied to the robot by the object, a coordinateconverting part for separating the rotational force component around thehorizontal axis and the translational force component in the horizontalback-and-forth direction, from the sensor signal of the force sensor, aforce-motion converting part for outputting these motion components,using a gain such as to reduce the resistance forces of the robot inthese rotational direction and translation direction to small values,based on the above-mentioned two force components, and a coordinateconverting part for synthesizing these motion components and outputtinga motion instruction to drive the robot arm.

In accordance with the controlling means for the cooperativeobject-transporting robot having the above-described constitution, whencontrolling the cooperative object-transporting robot which is arrangedso that a man and the robot grasp each of the ends of the object, andthat they transport the object sharing the load due to the weightthereof, it is possible to control so that the robot arm sharesapproximately a half of the weight of the object, by controlling thetranslational motion of the hand-tip in the vertical direction so as tokeep the posture of the object horizontal. Simultaneously, it ispossible to control the rotational motion of the hand-tip of the robotso that the rotational force at the hand-tip thereof becomes zero. As aforce sensor, it is essential only that one sensor for measuring a forceapplied to the robot arm by an object is provided. There is no need forsensor for measuring a force by an operator. Also, it is unnecessary toknow in advance the dimensions and the mass of the object.

Next, a second controlling method is a controlling method forcontrolling the cooperative object-transporting robot in order that aman and the robot transport a long object or a large-sized object in ahorizontal plane while grasping each of the ends thereof, and ischaracterized in that a force applied to the robot by the object isdetected by a force sensor, and that, based on the rotational forcecomponent around the vertical axis, and the translational forcecomponent in the direction of the object long axis obtained byconnecting the point grasped by the man and the point grasped by therobot, each of which is separated from the sensor signal, theabove-mentioned rotational motion component around the vertical axis andthe above-mentioned translational motion component in direction of theobject long axis are output, upon setting a gain so as to reduce theresistance forces of the object to small values, while the translationalforce component in the direction of the object short axis orthogonal toabove-mentioned object long axis is constrained so that no translationalmotion in the direction of the object short axis occurs, whereby amotion limitation equivalent to the object being supported by a virtualwheel facing the direction of the object long axis, at one point on therobot side, is imposed on the object, and then the robot arm is driven.Furthermore, in such a controlling method, the control may also beperformed on the precondition that an angle of the hand-tip of the robotis detected by angle sensors, and that, based on the sensor signals, amotion instruction for a translational motion of the hand-tip in thevertical direction is output so as to keep the posture of the objecthorizontal.

Moreover, a second controlling system is a controlling system forcontrolling the cooperative object-transporting robot in order that aman and the robot transport a long object or a large-sized object in ahorizontal plane while grasping each of the ends thereof, and ischaracterized by a force sensor for detecting a force applied to therobot by the object, a coordinate converting part for separating, fromthe sensor signal, the rotational force component around the verticalaxis, the translating force component in the direction of the objectlong axis obtained by connecting the point grasped by the man and thepoint grasped by the robot, and the translating force component indirection of the object short axis orthogonal thereto, a force-motionconverting part which, based on the above-mentioned rotational forcecomponent around the vertical axis and the above-mentioned translationalforce component in the direction of the object long axis, outputs thesemotion components, using a gain such as to reduce the resistance forcesof the robot in these rotational direction and translation direction,and a coordinate converting part for synthesizing these motioncomponents and the above-mentioned translational force component in thedirection of the object short axis which is set to be zero, andoutputting a motion instruction to drive the robot arm.

In accordance with the controlling means for the cooperativeobject-transporting robot having the above-described constitution, whencontrolling the cooperative object-transporting robot which is arrangedso that a man and the robot transport a long object or a large-sizedobject in the horizontal plane while grasping each of the ends thereof,a motion limitation equivalent to the object being supported by avirtual wheel facing the direction of the object long axis, at one pointon the robot side, is imposed on the object, and thereby the directionin which the object is movable is limited. This simplifies therelationship between the force applied by the operator and the motion ofthe object, and permits the operator to intuitively perceive thebehavior of the object by daily senses thereof. In addition, there is nofear of deviating from the original operational purpose of making theobject reach arbitrary target position and posture.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view for a cooperative object-transportingrobot controlled based on the present invention.

FIG. 2 is an explanatory view for the detected output component of theforce sensor used in a first control of the cooperativeobject-transporting robot in accordance with the present invention.

FIG. 3 is a construction view showing the first control system of thecooperative object-transporting robot in the present invention.

FIG. 4 is a conceptual explanatory view for a second control inaccordance with the present invention.

FIG. 5 is an explanatory view for the detected output component of theforce sensor used in the second control of the cooperativeobject-transporting robot in accordance with the present invention.

FIG. 6 is a construction view showing the second control system of thecooperative object-transporting robot in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

When a man and the robot cooperatively transport an object whilegrasping each of the ends of the object, the most important thing is howthe weight of the object is to be shared therebetween. In general, ifthe object is supported only by a translational force without applying atorque (rotational force) at the point where the object is supported, avertical force will be distributed in an inverse proportion to thedistance from the barycenter of the object. In many cases, a long objecthas a substantially uniform mass distribution, and hence, if no torqueis applied to the object by the tip of the robot and the tip of theobject is freely rotatable, the man and the robot will share the weightsubstantially half-and-half, irrespective of the mass and dimensions ofthe long object.

Meanwhile, in the transportation of a long object, the object will betransferred while keeping the posture thereof horizontal in the majorityof cases. It is therefore preferable that the vertical motion of therobot tip be controlled so that the tilt of the object is canceled out.Specifically, when the object tilts by being lifted by the man, the tiltof the object will be canceled out and the object will be able to keepthe posture thereof horizontal if the robot is caused to lift theobject, as well. The same goes for the case where the object is lowered.

With regard to a horizontal motion of the object, it is preferable thatthe robot move so as to copy after the force applied to the body by theman. That is, if virtual inertia and viscosity are set with respect tothe horizontal motion of the robot tip, and sufficiently low valuesthereof are selected, it will be possible to realize a motion copyingafter that of the man without providing a resistance force to the man.

Specifically, as shown in FIGS. 1 and 2, a force sensor 5 is providedbetween a robot arm 1 and a hand 2 disposed at the tip thereof, and bythis force sensor 5, a force applied to the robot arm 1 side by theoperator side Q via an object 4 is detected at an object-supportingpoint P on the robot side of the object 4. Then, the signal obtained isanalyzed into the translational force component Fx₁ in the horizontalback-and-forth direction (PQ direction), the translational forcecomponent Fz in the vertical direction (PR direction), and therotational force component τ₁ around the horizontal axis around thepoint P.

Although not shown in the figures, each of the joints of the robot armhas a joint actuator for driving each of the joints, and has an anglesensor for detecting the joint angle. A tilt angle θ of the object isdetected based on sensor signals of these angle sensors.

With regard to the translational force component Fx₁ in the horizontalback-and-forth direction and the rotational force components τ₁, thehorizontal velocity at the point 4 on the object and the rotationalvelocity at the hand-tip are determined so that the robot moves withoutresistance with respect to respective direction. Also, the verticalvelocity at the point P for making the posture of object 4 horizontal inproportion to the tilt angle θ of the object 4, is determined.

For these purposes, based on the rotational force component τ₁ aroundthe horizontal axis and the translational force component Fx₁ in thehorizontal back-and-forth direction in a sensor signal of the forcesensor 5, the robot arm is driven by outputting the rotational motioncomponent around the horizontal axis and the translational motioncomponent in the horizontal back-and-forth direction, upon setting again so as to reduce the resistance forces of the robot to small values.On the other hand, with regard to the hand-tip angle (tilt angle θ ofthe object 4) detected by the angle sensors at the hand-tip, a motioninstruction is output for a translational motion in the verticaldirection in proportion to the hand-tip angle, and thereby the hand-tipof the robot arm is driven upward and downward so as to keep the postureof the object horizontal.

In this way, around the point (point P in FIG. 2) where the robotsupports the object, since the object is freely rotatable and no torqueis applied to the object, the forces by the man and the robot in thevertical direction become substantially half-and-half in accordance withthe mass distribution of the long object. Also, when the man applies ahorizontal force to the object, the robot moves horizontally followingit without resistance. When the object tilts by being lifted by the man,a velocity upward in the vertical direction such as to make the tiltangle zero occurs in the hand-tip of the robot, and hence the objectrises while keeping the posture thereof horizontal. The same goes forthe case where the object grasped by the mans is lowered.

It can be said that such a control is a control in which an impedancecontrol is performed with respect to the horizontal direction while aninitial state of the object is maintained with respect to the verticaldirection.

In order to execute the above-described controlling method, a systemdescribed hereinafter with reference to FIGS. 2 and 3 may be used.

As shown in FIG. 2, the tip of a robot arm 1 need to have a hand 2 forgrasping an object 4 and a force sensor 5 for detecting a force appliedby an operator via the object 4. Also, as described above, each of thejoints of the robot arm has an joint actuator for driving each of thejoints, and has an angle sensor for detecting the joint angle.Meanwhile, as these joint actuators and angle sensors, those which aregenerally provided for robot arms which are subjected to a drivecontrol, are utilized as they are.

The sensor signal detected by the force sensor 5 is input to acontrolling system (computer). In this controlling system, as shown inFIG. 3, the translational force component Fx₁ in the horizontalback-and-forth direction, the translational force component Fz in thevertical direction, and the rotational force component τ₁ around thehorizontal axis are separated in a coordinate converting part (a).

On the other hand, in the angle sensor of each of the joints of therobot arm, a tilt angle θ of the object 4 is measured.

In a force-motion converting part, based on the above-describedtranslational force component Fx₁ in the horizontal back-and-forthdirection, the translational motion component (velocity andacceleration) in the PQ direction at the point P in FIG. 2 is determinedby the operation such as the following equation (1). Also, based on therotational force component τ₁ around the horizontal axis, the rotationalmotion component (angular velocity and angular acceleration) around thepoint P is determined by the operation such as the following equation(2). These are determined based on the setting of the gain such as toreduce the resistance forces of the robot in the rotation direction andthe translation direction to small values. $\begin{matrix}{{{Fx}_{1} = {{{{M\overset{¨}{x}} + {{Bx}\quad \overset{.}{x}}}->\overset{¨}{x}} = {{Fx}_{1} - \frac{{Bx}\quad \overset{.}{x}}{M}}}},\quad {\overset{.}{x} = {\int{\overset{¨}{x}{t}}}}} & (1) \\{{\tau_{1} = {{{{I\quad \overset{¨}{\theta}} + {{Bd}\quad \overset{.}{\theta}}}->\overset{¨}{\theta}} = \frac{\tau_{1} - {{Bd}\quad \overset{.}{\theta}}}{I}}},\quad {\overset{.}{\theta} = {\int{\overset{¨}{\theta}{t}}}}} & (2)\end{matrix}$

Here, in order to reduce the resistance forces of the robot to smallvalues, a target inertia coefficient M, a target inertia momentcoefficient I, a target viscous friction coefficient Bx, and a targetviscous friction coefficient Bd are each set to be low values.

On the other hand, based on the tilt angle which has been detected bythe angle sensors and which has been determined in a coordinateconverting part (b), the translational motion component (velocity) inthe vertical direction at the point P is determined in a motionconverting part, as being proportional to the tilt angle θ of theobject, as shown in equation (3).

{dot over (z)}=Kθ  (3)

A coordinate converting part (c) synthesizes the above-described motioncomponents, thereby determines the motion of the hand-tip of the robotarm 1, and outputs a motion instruction to drive each of the jointactuators. The motion of each of the joint actuators is detected by theangle sensor provided at each of the joints, and the position and thedriving velocity of each of the joints are fed back so that the motionof the robot arm approaches the target values.

Next, the second controlling means in accordance with the presentinvention will be described with reference to FIGS. 4 through 6. In thiscontrol, the following method and system may be constituted on theprecondition that the above-described hand-tip angle of the robot isdetected by the angle sensors, and that, based on the sensor signals, amotion instruction is output for a translational motion in the verticaldirection so as to keep the posture of the object horizontal.

Man frequently experiences daily an operation in which an object isplaced on a cart having passive wheels, and in which the object iscarried while the cart is pushed on a horizontal floor, when using asingle-wheel carrier (so-called “wheelbarrow”), a shopping cart, a babycarriage, a table wagon, or the like.

In these cases, the direction in which the cart is movable ismomentarily limited by the direction of the wheels. Specifically, in thedirection in parallel with the wheels, the cart can be moved to and froby the rotation of the wheels, but in the direction in orthogonal to thewheels, the cart cannot be moved unless the wheels are slipped sidewayagainst the friction between the floor surface and the wheels. Such akind of motion limitation is called a “nonholonomic constraint”.

Despite of such a limitation of the motion direction, it is possible toultimately make the cart reach arbitrary target position and posture bypushing the cart along an appropriate trajectory, and this has beenmathematically verified. In reality, man has generally a skill topractice it based on daily experiences.

As shown in FIG. 1, even when the hand 2 of the robot arm 1 and theoperator 3 grasp each of the sides of a long object or a large-sizedobject 4, and cooperatively transport it face to face in a horizontalplane, the man can intuitively perceive the behavior of the object ifhe/she controls the robot so that the object 4 conducts the samebehavior as that of the cart. This makes it possible to easily make theobject reach a target position and posture. For this purpose, asillustrated in FIG. 4, a motion limitation such that the object 4 issupported by a virtual wheel 6 facing the object long axis, on the robotside 4 a, is preferably imposed on the object 4. This permits theoperator side 4 b to perform the same operation as the case where theoperator side transports the object while pushing the cart in anappropriate direction which is exemplified by the arrow.

Specifically, as illustrated in FIG. 5, a force sensor 5 is providedbetween a rod arm 1 and a hand 2 disposed at the tip thereof, and bythis force sensor 5, a force applied to the robot arm 1 side by theoperator side Q via an object 4 is detected at one point P on the robotside of the object 4. Then, the signal obtained is analyzed into thetranslational force component FX₂ in the direction (PQ direction) of theobject long axis obtained by connecting the operator and the robot, thetranslational force component Fy in the direction (PR direction)orthogonal thereto, and the rotational force component τ₂ around thevertical axis at the point P. With regard to the rotational forcecomponent τ₂ and the translational force component Fx₂ in the long axisdirection, the robot is permitted to move without resistance withrespect to respective direction, while, with regard to the translationalforce component Fy, the motion of the robot is limited. This results inthat an equivalent motion limitation to the object 4 being supported bya virtual wheel facing the direction of the object long axis, at thepoint P, is imposed on the object.

For these purposes, based on the rotational force component τ₂ aroundthe vertical axis and the translational force component FX₂ in thedirection of the object long axis in a sensor signal of the force sensor5, the rotational motion component around the vertical axis and thetranslational motion component in direction of the object long axis areoutput, upon setting a gain so as to reduce the resistance forces of therobot to small values. On the other hand, the translational forcecomponent Fy in the direction of the object short axis is constrained sothat no translational motion in the direction of the object short axisoccurs, and then the robot arm is driven. Herein, this constraint forpreventing the translational motion component in direction of the objectshort axis from occurring is achieved by outputting the motioninstruction such that the motion component in the direction of theobject short axis becomes substantially zero.

In this way, the point P on the object 4 shown in FIG. 5 is permitted totranslate only in the PQ direction. In addition, the point P ispermitted to be rotated therearound. Furthermore, the point P is alsopermitted to successively vary the travelling directions thereof whileproceeding along a smooth curved trajectory tangent to the straight linePQ. Since the behavior of the object 4 is the same as the case where itis supported by the wheel at the point P, the operator can intuitivelymake the object reach a target position and posture, using the sameskill as the case where the operator pushes a cart.

In order to execute the above-described first controlling method, asecond system described hereinafter with reference to FIGS. 5 and 6 maybe used.

As shown in FIG. 5, the tip of the robot arm 1 need to have a hand 2 forgrasping an object 4 and have a force sensor 5 for detecting a forceapplied by an operator via the object 4. The sensor signal detected bythe force sensor 5 is input to a controlling system (computer). In thiscontrolling system, as shown in FIG. 6, the translational forcecomponent Fx₂ in the direction of the object long axis, thetranslational force component Fy in the direction of the object shortaxis, and the rotational force component τ₂ around the vertical axis areseparated in a coordinate converting part (1).

In a force-motion converting part, the translational motion component(velocity and acceleration) in the PQ direction at the point P in FIG. 5is determined based on the above-described translational force componentFx₂ in the direction of the object long axis, and the rotational motioncomponent (angular velocity and angular acceleration) around the point Pis determined based on the rotational force component τ₂ around thevertical horizontal axis. The determination of these motion componentsis based on the setting of a gain such as to reduce the resistanceforces of the robot in the rotation direction and the translationdirection to small values. On the other hand, with regard to thetranslational force component Fy in the direction of the short axis, thetranslational motion component (velocity and acceleration) in the PRdirection, at the point P, is set to be zero irrespective of the outputof the force sensor. These motion components are synthesized in aforce-motion converting part (2), and a motion instruction to drive eachof the joint actuators of the robot arm 1 is output. The motion of eachof the joint actuators is detected by an angle sensor provided at eachof the joints, and the position and the driving velocity of each of thejoints are fed back so that the motion of the robot arm approaches thetarget values.

What is claimed is:
 1. A method for control a cooperativeobject-transporting robot, in which a man and a robot transport a longobject or a large-sized object in a horizontal plane while grasping eachof the ends of the object, wherein: a force applied to the robot by theobject is detected by a force sensor, and based on the rotational forcecomponent around the vertical axis, and the translational forcecomponent in the direction of the object long axis obtained byconnecting the point grasped by the man and the point grasped by therobot, each of which is separated from the sensor signal, saidrotational motion component around the vertical axis and saidtranslational motion component in the direction of the object long axisare output, upon setting a gain so as to reduce the resistance forces ofthe object to small values, while the translational force component inthe direction of the object short axis orthogonal to said object longaxis is constrained so that no translational motion in the direction ofthe object short axis occurs, whereby a motion limitation equivalent tothe object being supported by a virtual wheel facing the direction ofthe object long axis, at one point on the robot side, is imposed on theobject, and then the robot arm is driven.
 2. A method as claimed inclaim 1, wherein: an angle of the hand-tip of the robot is detected byangle sensors, and based on the sensor signals, a motion instruction fora translational motion of the hand-tip in the vertical direction isoutput so as to keep the posture of the object horizontal.
 3. A systemfor control a cooperative object-transporting robot, in which a man anda robot transport a long object or a large-sized object in a horizontalplane while grasping each of the ends of the object, said systemcomprising: a force sensor for detecting a force applied to the robot bythe object; a coordinate converting part for separating, from the sensorsignal, the rotational force component around the vertical axis, thetranslating force component in the direction of the object long axisobtained by connecting the point grasped by the man and the pointgrasped by the robot, and the translating force component in directionof the object short axis orthogonal thereto; a force-motion convertingpart which, based on said rotational force component around the verticalaxis and said translational force component in the direction of theobject long axis, outputs these motion components, using a gain such asto reduce the resistance forces of the robot in these rotationaldirection and translation direction; and a coordinate converting partfor synthesizing these motion components and said translational forcecomponent in the direction of the object short axis which is set to bezero, and outputting a motion instruction to drive the robot arm.